(a) Field of the Invention
The present invention relates to a novel fulvene compound and a preparation method thereof, and more particularly to a fulvene compound having substituted groups in the 2- and 5-positions prepared from an unsaturated ketone having a substituted group in the β-position and a halogen atom in the α-position, and a preparation method thereof. The present invention also relates to a metallocene catalyst having a substituted group in the α-position carbon of the bridge of the cyclopentadienyl group made only by reaction of a fulvene compound and an anion group including the cyclopentadienyl group, and a preparation method of a olefin copolymer using the same.
(b) Description of the Related Art
The fulvene compound is a very important intermediate for synthesizing natural product s or transition metal catalysts having cyclopentadienyl groups. A variety of information is given in Chemical Review, 1968, 68, 41 regarding the synthesis and reaction of fulvenes.
In general, fulvene is prepared by the reaction of a cyclopentadiene anion and a ketone or an aldehyde. The cyclopentadiene anion may be reacted with an electrophilic carbonyl compound, or cyclopentadiene may be reacted with an electrophile in the presence of a base such as sodium ethoxide.
Also, the Wittig reaction can be used. However, the most recent preparation method is to obtain a fulvene derivative by reacting a cyclopentadiene derivative with an electrophile in the presence of pyrrolidine (Journal of Organic Chemistry 1984, 49, 1849).
The fulvene compound can be purified by column chromatography for a smaller scale, and by distillation or recrystallization for a larger scale.
Generally, a fulvene compound is prepared by the following Schemes 1 and 2:


In Schemes 1 and 2, the fulvene derivative may or may not have substituents on the pentagonal ring. In the conventional method, it is impossible to add substituted groups at the 2- and 5-positions of the pentagonal ring simultaneously, because a cyclopentadienyl anion or cyclopentadiene having a substituent is reacted with a ketone or an aldehyde. That is, in Scheme 1, the substituent is mainly added to the β-position instead of α-position of the cyclopentadiene due to steric hindrance. Also, in Scheme 2, when a cyclopentadienyl anion having two substituents in the 1- and 3-positions is reacted with an electrophile, a fulvene having substituents at the α- and β-positions is produced exclusively, but one having substituents at both α-positions is not produced.
A group 4 transition metal compound having one or two cyclopentadienyl group(s) as a ligand may be activated with methylaluminoxane or a boron compound to be used as an olefin polymerization catalyst (U.S. Pat. No. 5,580,939). This catalyst shows unique characteristics that cannot be offered by the conventional Ziegler-Natta catalyst. That is, it has a narrow molecular weight distribution, offers good reactivity to secondary monomers such as α-olefins or cyclic olefins, and the prepared copolymers have a uniform secondary monomer distribution. Moreover, stereoselectivity can be controlled by changing the substituent of the cyclopentadienyl ligand during α-olefin polymerization (Angew. Chem. Int. Ed. Engl. 1995, 34, 1143), and the degree of copolymerization, molecular weight, secondary monomer distribution, etc. can be controlled during copolymerization of ethylene and other olefins (U.S. Pat. No. 5,470,811).
With the development of catalyst systems, efforts to find catalysts suitable for copolymerization of ethylene and an α-olefin (LLDPE, VLDPE, EPM, and EPDM), for copolymerization of ethylene and a cyclic olefin, for copolymerization of an α-olefin and a cyclic olefin [cyclic olefin copolymer (COC)], and for copolymerization of ethylene, α-olefin, and styrene, are continuously being made. Such copolymerization requires catalysts with good activity, superior reactivity for the secondary monomer, and uniform secondary monomer distribution.
Other than the Ziegler-Natta catalyst, metallocene catalysts are used for such copolymerization. Because the metallocene catalyst is more expensive than the Ziegler-Natta catalyst, it should have good activity to be economically viable. If the metallocene catalyst has good reactivity for the secondary monomer, it is possible to obtain a polymer comprising a lot of secondary monomers with a small amount of catalyst.
As a result of much research on copolymerization using a variety of catalysts, it has been proved that ansa-type metallocene catalyst has good reactivity for the secondary monomer in general. According to F. J. Karol's research, when producing an LLDPE with a density of 0.93 using hexene as a secondary monomer in the presence of a bridged catalyst, an ethylene/hexene ratio of 0.004 to 0.005 is sufficient. However, for a non-bridged catalyst, the ethylene/hexane ratio should be at least 0.02 (1997. 4. 18. US Palm Coast, Fla., Polymer Reaction Engineering Foundation Conference).
Therefore, the catalyst having bridged ligand structure has attracted interest. Also, the catalyst having bridged ligand structure can control the molecular structure of the propylene polymer depending on the molecular symmetry.
The catalysts having bridged ligand structure developed thus far can be classified into three types depending on the bridge type. The first is a catalyst in which two cyclopentadienyl ligands connected by the reaction of indene or fluorene with an electrophile such as an alkyl halide; the second is a silicon bridged catalyst connected by —SiR2—; and the third is a methylene bridged catalyst obtained by the reaction of fulvene and indene or fluorene. The following Schemes 3 to 5 are representative syntheses for these catalysts.



There are two major factors that affect the activity of the metallocene catalyst and the stereostructure of the polymer. One is the steric hindrance of the catalyst, which determines how freely the monomer can approach the catalyst, and the other is the electronic effect, which determines how much the activated catalyst can be stabilized. If an electron-donating substituent such as an alkyl group is substituted on the cyclopentadienyl ring, it stabilizes the activated metallocene catalyst, and therefore offers advantages to polymerization.
A variety of metallocene catalysts are prepared using common fulvene compounds as an intermediate. Among such catalysts are the metallocene derivatives having a cyclopentadienyl group and a fluorenyl group, which are prepared by Scheme 5. Among them, the one with the least steric hindrance is the one having no substituent on the cyclopentadienyl group (U.S. Pat. No. 5,087,677). However, since the metallocene catalyst prepared by this method has no alkyl substituent, it has an insufficient electronic effect.